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Old 03-01-2012, 08:10 PM
78_f150 78_f150 is offline
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Dual battery wiring

My daily driver is a 78 crewcab and im hooking up dual batterys. As i have it right now i have both wired positive to positive and then both grounded to the block. Works fine, but i want to have the second battery isolated so i can never be left with a dead battery.

been doing tons of reading and i know i can buy a battery isolator but ive also seen people wiring up a second solenoid and a switch in the cab.

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Now if i wire a solenoid and a switch, will the aux battery stay charged? Lets say i leave the radio on or key on and main battery dies and wont crank. flip the switch in the dash and im cranking off the aux battery? will this setup leave the aux battery always charged so i will never be stranded?

I have a stereo in the truck and a winch on it and i have been left with a dead battery before and i just never want to be left out with a dead battery.
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Old 03-01-2012, 08:35 PM
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Based on that circuit, turning off the ignition will de-energize the continuous duty solenoid and isolate the aux battery.

So you're asking if that circuit will allow you to self jump?

In that case, no... not if the main battery is completely dead. Why? The continuous duty solenoid will not energize because it is connected through to the rocker switch, the ignition switch, and then the main battery (which we assume is completely dead).

However, if the main battery is not completely dead, then yeah, the solenoid can energize and connect the aux battery to the main battery (in parallel).

I suggest the rocker connect to a relay sourcing power from by the ignition switch to automatically energize the solenoid. This would be the normal position. Then other side of the three-position switch sourcing power from the aux battery as the self-jump position. Center would be both circuits disconnected.
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Old 03-01-2012, 09:19 PM
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Do yourself a favor and get a battery isolator. They are cheap, easy to install and pretty much foolproof. I have a separate battery installed for my plow and aircraft landing lights (for seeing when it's REALLY snowing), and if I ever need a jump, it's right there under the hood. I bought mine at a garage sale for $5. Been in for twenty years with no problems. The problem I see with your diagram is that if you accidentally leave the aux battery switch off, you'll get no charge. If you leave the switch on and your main battery dies, so will the aux. Why deal with all the "stuff"? An isolator will keep your aux battery charged, but will not let it discharge in case you have a drain on your regular battery.
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Old 03-01-2012, 09:23 PM
78_f150 78_f150 is offline
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So if i get a battery isolator thats going to keep the aux battery charged. Now what happens if i get a dead battery? Also im going to be installing some lights and i have a winch as well. Would i be best off wiring those to the aux battery?

Basically I never want to be left with a dead battery.
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Old 03-01-2012, 09:31 PM
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From the factory that's the way it was wired. With the ignition "on" the solenoid for the aux. battery was energized and connected the battery to the electrical system to charge it. When the key was switched "off" the solenoid de-energized and disconected the battery from the system, that way you could run your camper off the auxilliary battery and not worry about running the main battery down.
The auxilliary battery was originally designed to power a camper, not as an additional battery for starting.
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Old 03-01-2012, 09:33 PM
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Originally Posted by 78_f150 View Post
So if i get a battery isolator thats going to keep the aux battery charged. Now what happens if i get a dead battery? Also im going to be installing some lights and i have a winch as well. Would i be best off wiring those to the aux battery?

Basically I never want to be left with a dead battery.
Wow...fast response. I hope I answered your questions. I love mine. I used to see my main battery get VERY weak if I used the plow and lights a lot. Alternator had trouble keeping up when the engine was "stop and go" during plowing.

Yes....wire everything that is not essential when you are doing normal driving off of the aux battery. That will keep the main battery load to a minimum and increase the odds of getting a good strong start every time. If you do get a dead main battery, chances are the aux will be good enough to give yourself a jump. Mine has saved me a few times when I left the headlights on. You could still wire in a solenoid to give yourself the jump, but for as often as it happens it would probably be wasted effort, and if you forgot to turn it off, you'd be right back where you started.
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Old 03-01-2012, 09:42 PM
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Quote:
Originally Posted by mikeo0o0o0 View Post
From the factory that's the way it was wired. With the ignition "on" the solenoid for the aux. battery was energized and connected the battery to the electrical system to charge it. When the key was switched "off" the solenoid de-energized and disconected the battery from the system, that way you could run your camper off the auxilliary battery and not worry about running the main battery down.
The auxilliary battery was originally designed to power a camper, not as an additional battery for starting.
Thats how the local electric guy was explaining it to me. So when i have the truck running it is charging the aux battery but nothing is being drawn off it. When i turn it off then its disconnected from the main and lets say i turned on my driving lights or i ran my winch i would be running off the aux battery?

Really what i want to do is never be left with a dead battery anywhere.
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Old 03-01-2012, 09:46 PM
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Yup...that's how it works. No promises that you'll never have a dead battery, but if you carry a set of jumper cables and you don't run the "aux" stuff with the engine off for too long, you should seldom, if ever, be stranded with a "no start" battery condition. The difference is that with an isolator, it does the same thing, but YOU don't have to do anything. It's all taken care of for ya.
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Old 03-01-2012, 10:02 PM
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so if i wire up a battery isolator and my main battery dies then it will automatically draw off the aux battery and start up?
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Old 03-01-2012, 10:07 PM
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Originally Posted by 78_f150 View Post
so if i wire up a battery isolator and my main battery dies then it will automatically draw off the aux battery and start up?
No...you will have to use a set of jumper cables from the aux battery to the dead battery. That's the whole point. A discharge on the main battery will not kill the aux, and vice versa. The isolator will make it seem like you have two separate batteries, but they will both stay charged. Cool!
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Old 03-01-2012, 10:32 PM
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No...you will have to use a set of jumper cables from the aux battery to the dead battery. That's the whole point. A discharge on the main battery will not kill the aux, and vice versa. The isolator will make it seem like you have two separate batteries, but they will both stay charged. Cool!
Ok that makes sense!

Now if i wire it up with a solenoid, then while the trucks running its charging the aux battery but with the truck off the aux battery is disconnected? so if i hook my lights and accesories to the aux battery and it dies, when i start the truck it will start off the main battery and then charge the aux battery?

But lets say i want to listen to my stereo with the truck not running. do i just have the stereo wired to the aux battery?
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Old 03-01-2012, 10:44 PM
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FYI: Here's a write-up on a dual battery installation that answer most of your questions: Dual Battery Installation
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Old 03-01-2012, 10:50 PM
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Ok that makes sense!

Now if i wire it up with a solenoid, then while the trucks running its charging the aux battery but with the truck off the aux battery is disconnected? so if i hook my lights and accesories to the aux battery and it dies, when i start the truck it will start off the main battery and then charge the aux battery?

But lets say i want to listen to my stereo with the truck not running. do i just have the stereo wired to the aux battery?
Yes to the first..it will disconnect the aux with the key off. Yes to the second..when you start the truck, it will recharge both. No to the third...not unless you listen for a LONG time. Anything on the main battery will draw current and eventually kill it, so anything you want to use, but not drain the main battery, wire to the aux. Stereos are not big current loads, unless you have those thunder boxes that annoy all of the cars within a half mile. Wipers, fans, lights, etc. are the battery killers. But keep in mind that if you kill the aux and the main is too low to start the truck, you're stranded. These things aren't magic. Just a way to use more electrical accessories without overloading the main battery. Also, be aware that your alternator is now charging two batteries at the same time, so if both are really low, it could overheat. I've never had a problem with mine, but it's a heavy duty alternator.
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Old 03-01-2012, 10:53 PM
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ok makes sense now.I have the biggest heavy duty alternator and a new regulator on the truck. I think i will go with an isolator sounds like it will work fine. I have a full stereo and run 2 amplifiers one for sub woofers and one for the speakers. so it does drain the battery very quick.
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Old 03-02-2012, 04:53 PM
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I'd do that, but instead of the noid, I'd put a manual isolator switch in (only problem is that in order to have the switch in the cab, you have to run that heavy *** power cable up to the cab too)
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Old 03-02-2012, 04:53 PM
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